The present invention relates to packages for protecting comestibles. More specifically, it relates to films and molded containers which are formed from polyesters.
Presently there is a strong interest in the packaging industry for protecting comestibles (such as foodstuffs, medicines, and especially carbonated beverages) by enveloping the substances in packages which are formed from various polymers. One polymer in which there is an especially strong interest is polyethylene terephthalate. Containers formed from this material, which may be biaxially oriented, possess many desirable characteristics. Molded biaxially oriented containers which are formed from polyethylene terephthalate and certain copolyesters are disclosed in U.S. Pat. No. 3,733,309. While molded containers formed from polyethylene terephthalate have, as indicated, many desirable characteristics, there is a need in the art to provide improved polyester containers which will have gas permeabilities which are lower than those of containers formed from polyethylene terephthalate. Such improved containers would be much more versatile in their utilization and allow the containers to be used to package substances for which the polyethylene terephthalate containers may not be suitable.
The present invention provides such an improved container. The container of the present invention is formed from a polyester resin which incorporates diacid units derived from iminodiacetic acid, oxydiacetic acid, or thiodiacetic acid.
U.S. Pat. No. 3,991,035 discloses a process for preparing filaments of a linear glycol terephthalic polyester. The process comprises modifying the polyester by incorporating therein units which may be derived from iminodiacetic acid and thiodiacetic acid. A comparative example also discloses polyesters which incorporate oxydiacetic acid. However, there is no disclosure nor suggestion in this patent specification that such polyesters can be formed into sheet, film, or molded articles. Because such articles could not be known or contemplated from a reading of this disclosure, there is likewise no disclosure nor suggestion of the improved gas barrier properties which make containers formed from these or related compositions useful in the packaging industry.
It has now been found that containers which are formed from specified polyester compositions exhibit desirable physical properties, including improved gas barrier properties, which render them advantageous for use in the packaging of comestibles.